In most cases, it depends on where they lived. If they lived here at
Fermilab, chances are they don’t go anywhere at all.

In the southern end of the Tevatron ring, near DZero,
there is a veritable forest of dead trees. Their number
is uncertain, but they definitely outnumber live ones.

“Not only is it unsightly,” said Dmitri Denisov, who
works at DZero and gives about one tour of the
facility each month, “but it also raises some
uncomfortable questions.”

Those questions, Denisov said, come from visitors
who seem to be concerned that the trees—which are
mostly inside the accelerator ring—are being killed off
by radiation.

Of course, this is not the case. The trees, mainly
cottonwoods, are being killed off by the Ecological
Land Management Committee. Some of the trees
have been killed by the annual prairie burn, and some
have been girdled, which involves making a cut
around the circumference of the tree to prevent
nutrients from circulating. A girdled tree usually dies
within a year or two.

Those trees were never supposed to be there in
the first place. The land inside the ring is prairie
land, or at least it’s supposed to be, and prairies don’t have trees. But
cottonwoods are a weedy, aggressive species, and they’ve invaded
the southern end of the ring.

“There are good places for trees and bad places for trees,” said Peter
Kasper, a Fermilab physicist and ELM bird monitor. Grasslands and
prairies are bad places for trees.

Birds such as the Grasshopper Sparrow or the Meadowlark, Kasper said,
won’t nest anywhere near a tree for fear of predators. If a tree ends up in
the middle of prime grassland, that grassland will be ruined for many
animals that otherwise would like to live there.

“There are GOOD PLACES FOR TREES and BAD PLACES FOR TREES”

Beginning in the mid-80s, ELM started paying
careful attention to where trees were planted in
the lab, and now there is a detailed plan—online
at www-esh.fnal.gov/ELM/ELM_Plan_2002.htm
—for each of Fermilab’s 6,800 acres. The northwest
corner of the lab is being converted to woods—
trees are regularly planted in those areas, and
valuable trees like oaks are relocated there (rather
than killed) whenever possible. The plan for the
ring calls for getting rid of the cottonwood grove
and converting the land there to restored prairie.

If that grove of trees—or any grove of trees—
is instead left to its own devices, it will eventually
kill the prairie, as the trees grow and choke out the
shorter grasses. Fires traditionally kept the woody
areas at bay (if you look at pre-settlement habitat
distributions, you’ll notice forested areas generally
developed around rivers and other natural fire
breaks). But natural prairie fire is a rarity these
days, and land managers interested in prairie
restoration have had to find other means of
controlling the spread of trees.

The most familiar method is probably the controlled
prairie burn, but others include mowing and tree
removal. These are part of an overall strategy
known as “ecosystem management,” or EM,
adopted by ELM in the last five to 10 years.
It was a broad strategy until recently, but now a
four-person subcommittee makes decisions on a
tree-by-tree basis to help the overall plans along.

The goal of this strategy, said committee member
Rod Walton, “is a full-scale reconstruction of
a functional ecosystem that is as close to
pre-settlement conditions as possible.”

And that means that prairie needs to be prairie,
and woods need to be woods.

Which brings us back to that forest of dead trees,
and why it’s not going anywhere.

“Tree removal is always dangerous,” said
Mike Becker of Fermilab’s Roads and Grounds
department, which does the actual work of cutting
them down. “You’re using chainsaws and heavy
equipment.”

Despite the risk, the trees would be removed if they
were near roads or buildings, or someplace where
people go regularly—”basically anywhere they’d
threaten infrastructure,” Becker said. This approach
isn’t unique to Fermilab. Spokespersons for both
the Morton Arboretum and the DuPage County
Forest Preserve said they have similar policies.
But since the trees in question are in a natural
area, there’s no real reason to cut them down.

“The only drawback to leaving them there is
looks,” Walton said. “They provide food and
shelter for insects and birds, and when they
decay they provide humus for the soil.” Humus
is dark, rich, fertile soil produced by the decay
of organic material. Many people buy it to use
as fertilizer for their gardens. In the meantime,
Kasper said, the dead trees keep woodpeckers
out of the power poles and provide convenient
perches for hawks.

“It’s not so much a matter of educating the
public,” Kasper said, “but of educating ourselves.
A lot of people interact with the public...They
should know we’re actually managing the land
intelligently and with a purpose and—importantly
for this place—in a way that has some science
behind it.”